Aging Microstructure and Creep Rupture Properties of Super304H Steel Welded Joint

Super304H steel welded joint was aged at 700℃ for different times (100, 300, 500 h), and the aging microstructure and impact property of the welded joint was investigated. The creep rupture properties of the welded joint at 700℃ under different stresses were analyzed. The results show that after aging at 700℃ for 100 h, granular, hammer-like and strip-like M₂₃C₆ phase precipitated from grain boundaries and dendritic grain boundaries of austenite in the Super304H steel welded joint, and impact toughness of the welded joint decreased apparently. With the increase of aging time, precipitating rate of M₂₃C₆ phase slowed down and the impact toughness became stable. The creep rupture sample of welded joint all fractured at the position of base material, and obvious necking occurred before fracture. The fracture mainly showed transgranular characteristic when the loading stress (180 MPa) was relatively high, and changed into intergranular characteristic when the loading stress (160 MPa) was relatively low.